System and method for cooperative robotics

ABSTRACT

A method performed in a system comprising a plurality of autonomous vehicles. The method comprises a first vehicle transmitting a geometric configuration information to be adopted by one or more other vehicles participating in a transport operation in combination with the first vehicle, wherein the geometric configuration information comprises information regarding respective distances and orientations the one or more other vehicles are required to adopt relative to the first vehicle, a second vehicle, upon receipt of the geometric configuration information, adopting a position relative to the first vehicle or to a further vehicle participating in the transport operation, the position of the second vehicle defined by the geometric configuration information and the first and second vehicles performing a transport operation in a synchronised manner once the second vehicle has adopted said position.

FIELD

Embodiments described herein relate generally to distributed transportand more particularly to information exchange between members of a groupof devices participating in distributed transport.

BACKGROUND

Future industrial systems are projected to encompass enhanced automationand increased penetration of mobile robots. The logistic sector isalready employing mobile robots, particularly in warehouse and containerterminals. Current industrial applications are mostly focused on asingle mobile robot.

The use of multiple mobile robots or a network of mobile robots, actingin a collaborative/cooperative manner, improves efficiency andperformance of industrial operations. Moreover, it creates newopportunities for automation processes targeting complex manipulativetasks. Cooperative robotics is also attractive from an economicperspective as multiple identical robots can be used (for transportingdifferent sized objects) which are cheaper to produce and maintain ascompared to different-sized robots which are used in variousstate-of-the-art warehouse applications.

Arrangements of the embodiments will be understood and appreciated morefully from the following detailed description, made by way of exampleonly and taken in conjunction with drawings in which:

FIG. 1 shows a warehousing environment in which the present system canbe operated;

FIG. 2 shows an example of a transport robot;

FIG. 3 shows and example of a central control unit;

FIG. 4a ) illustrates the communication of task information to a groupof robots;

FIG. 4b ) illustrates the election of a leader from among the group ofrobots;

FIG. 4c ) illustrates the recruitment of followers following leaderselection;

FIG. 5 illustrates selection of a leader based on geometric and batterycharge considerations;

FIG. 6 show a signalling procedure for collective transport groupcommunication;

FIG. 7 illustrates show a signalling procedure for collective transportgroup communication incorporating neighbour to neighbour signalexchange;

FIG. 8 illustrates examples of different geometric formations;

FIG. 9 illustrates examples of geometry matrices for different geometricformations;

FIG. 10 illustrates mapping generate by the leader robot;

FIG. 11 illustrates a reference matrix generated by the leader robot;

FIG. 12 illustrates subsequent reference matrices generated on the flyby the leader robot;

FIG. 13 illustrates a signalling process used in maintaining an adoptedformation using closed loop interaction; and

FIG. 14 illustrates a process for formation reconfiguration followingloss of a robot.

DETAILED DESCRIPTION

According to an embodiment there is provided a method performed in asystem comprising a plurality of autonomous vehicles. The methodcomprises a first vehicle transmitting a geometric configurationinformation to be adopted by one or more other vehicles participating ina transport operation in combination with the first vehicle, wherein thegeometric configuration information comprises information regardingrespective distances and orientations the one or more other vehicles arerequired to adopt relative to the first vehicle, a second vehicle, uponreceipt of the geometric configuration information, adopting a positionrelative to the first vehicle or to a further vehicle participating inthe transport operation, the position of the second vehicle defined bythe geometric configuration information and the first and secondvehicles performing a transport operation in a synchronised manner oncethe second vehicle has adopted said position.

The first and second vehicle may perform the transport operation inresponse to the first vehicle sending a triggering signal to start thetransport operation.

In an embodiment the one or more vehicles, upon receipt of the geometricconfiguration information, return information indicating one or more of:a distance of the individual vehicle to each location identified in thegeometric configuration information or an amount of energy available tothe vehicle. The first vehicle assigns an individual one of the furthervehicles to each said location based on said returned information.

In an embodiment the second vehicle, upon receipt of said geometricconfiguration information, assign itself to a location identified in thegeometric configuration information based on at least one of: a distanceof the second vehicle to the location, an amount of energy available tothe vehicle or an estimated amount of energy required for the transportoperation.

In an embodiment throughout the transport operation the first vehicletransmits movement information to other vehicles participating in thetransport information indicating a next movement required to beperformed by the other vehicles. The movement information is such thatrelative positions of the vehicles participating in the transportoperations are maintained whilst the vehicles perform the next movement.

In an embodiment the movement information comprises a velocity to beadopted by the vehicles and wherein the vehicles feed a current velocityback to the first vehicle.

In an embodiment the one or more of the vehicles participating in thetransport operation comprise a sensor or sensors for sensing one or moreenvironmental conditions and a transmit function for communicating asensed environmental condition to other vehicles participating in thetransport operation.

In an embodiment the first vehicle stops or pauses the transportoperation upon receipt of information from a vehicle participating inthe transport operation indicating an environmental conditiondetrimental to continuing the transport operation.

In an embodiment, upon receipt of information indicating that a vehiclethat had previously participated in the transport operation is not ableto complete said transport operation, said first vehicle eitherinstructs remaining vehicles participating in the transport operation toadopt a geometric configuration suitable for completion of the transportoperation and requiring a reduced number of vehicles or recruit areplacement vehicle for participation in the transport operation.

In an embodiment the vehicles participating in the transport operationcommunicate using a transmission schedule consisting of timeslots ondistinct frequency channels based on handshakes between the firstvehicle and the vehicles participating in the transport operation.

The first vehicle may assign priorities for requesting timeslots ondistinct frequency channels to the other vehicles participating in thetransport operation.

The first vehicle may assign one or more timeslots on a distinctfrequency channel for communication with all follower vehicles.

A vehicle participating in the transport operation may request one ormore timeslots on a distinct frequency channel for communication withthe first vehicle or another vehicle of the vehicles participating inthe transport operation, with the first vehicle confirming the requestonly if it does not find another vehicle participating in the transportoperation and using the same timeslot on the same frequency channel.

The assigned timeslot of the transmission schedule may be used by thevehicle participating in the transport operation to report at least oneof a distance from the first vehicle or from another vehicleparticipating in the transport operation or a battery level.

In an embodiment a vehicle participating in the transport operationselects another vehicle participating in the transport operation as areference vehicle for maintaining a formation indicated by the geometricconfiguration information, wherein the selection is based on informationreceived from other vehicles participating in said transport operation.

The vehicles in the system may have identical size and/or liftingability or may be differently sized or have different lifting ability.

The vehicles may be earth bound based robots, drones, cooperative robotsor automatic guided vehicles. The vehicles may operate in a warehouse orother logistics environment.

In an embodiment there is provided a system comprising a plurality ofautonomous vehicles. The system comprising a first vehicle configured totransmit geometric configuration information to be adopted by one ormore other vehicles participating in a transport operation incombination with the first vehicle, wherein the geometric configurationinformation comprises information regarding respective distances andorientations the one or more other vehicles are required to adoptrelative to the first vehicle, a second vehicle configured to, uponreceipt of the geometric configuration information, adopt a positionrelative to the first vehicle or to a further vehicle participating inthe transport operation, the position of the second vehicle defined bythe geometric configuration information and the first vehicle and thesecond vehicle configured to performing a transport operation in asynchronised manner once the second vehicle has adopted said position.

In another embodiment there is provided an autonomous vehicle configuredto transmit geometric configuration information to be adopted by one ormore other vehicles participating in a transport operation incombination with the autonomous vehicle, wherein the geometricconfiguration information comprises information regarding respectivedistances and orientations the one or more other vehicles are requiredto adopt relative to the first vehicle.

In another embodiment there is provided computer program instructionsfor execution by a processor, the computer program instructionsconfigured to cause the processor, when executing the computer programinstructions, to perform any of the methods described herein, be that amethod performed by the entire system or a method performed by anindividual component or vehicle of the system.

Mobile robots play an important role in various industrial applications.The logistic sector, for example, is using mobile robots, for example inwarehouses and container terminals. Existing applications are based onthe use of a single robot. The use of multiple mobile robots or anetwork of mobile robots in embodiments, acting in acollaborative/cooperative manner, provides various performanceenhancements and benefits. The problem of collaboratively transportingan object, also referred to as the collective transport problem,involves synthesis/formation of an appropriate geometric pattern forefficiently carrying the object. Moreover, this pattern should bemaintained while transporting the object from one point to another. Theframework disclosed herein leverages local sensing capabilities andultra-low latency wireless communication for efficient formationsynthesis and control. The proposed framework is completely distributedin nature and does not rely on a global coordinate system for mobilerobots. It displays generality in terms of produced geometric formationsand ensures stability of formation from any initial states. It alsoprovides necessary formation robustness for operation in dynamicenvironments characterized by the presence of obstacles.

The problem of collaboratively transporting an object, also referred toas the collective transport problem, involves synthesis/formation of anappropriate geometric pattern for efficiently carrying the object.Moreover, this pattern must be maintained while transporting the objectfrom one point to another.

Existing techniques for pattern formation often rely on complex sensorycapabilities and control designs, and may not take into account thepossibility of information exchange among robots. Ultra-low latencywireless communication can improve the convergence time of synthesizinga formation as well as reconfiguration time of the formation of mobilerobots. Protocols that achieve ultra-low latency are described herein.Moreover, it also reduces sensory and processing overhead, which isparticularly attractive for minimizing energy consumption ofbattery-operated robots.

The framework disclosed herein leverages local sensing capabilities,such as, for example, capabilities provided by the use of cameras, UWBsensors (although embodiments may comprise all other suitable means ofsensing a part of an environment local to the vehicle), and ultra-lowlatency wireless communication for efficient formation synthesis andcontrol. The disclosed framework is completely distributed in nature anddoes not rely on a global coordinate system to allow mobile robots tosynthesise a given formation. This said, each robot/vehicle is aware ofa reference direction (for example North) that is the same for allrobots in the system. Embodiments are not limited in terms of thegeometric formations that can be produced. Geometric formations can bestably maintained irrespective of the formation and/or the initialstates of the robots. Embodiments also provide desired formationrobustness for operation in dynamic environments characterized by thepresence of obstacles. In embodiments obstacles are dealt with invarious ways. One way is to stop the formation in case a moving obstaclecomes on the way (e.g., a human or another robot). This is achievedthrough an emergency message leveraging group communicationcapabilities. For static obstacles, the formation may be reconfigured toa formation that can move around the obstacle.

A warehouse 100 with plurality of mobile robots and platforms/pallets(in which inventory items are placed) and in which embodiments can beused is shown in FIG. 1. Goods may be received at an incoming goodsentry 110. To store the goods, they are to be transported to a storagearea 120. It will be appreciated that this storage area 120 may be inany part of the warehouse 100 or may indeed cover the entire warehouse100. A plurality of robots 130 are provided to transport platforms 140on which goods to be transported may be arranged form the incoming goodsection 110 to the storage area 120. The platforms 140 are provided indifferent sizes to accommodate different sizes of goods or differentquantities thereof. When not active the robots may be stored in a robotstation 150. The station may comprise a charging facility that allowsthe robots to re-charge a battery needed for their operation. Aplurality of obstacles 160 may be present within the warehouse 100 andhuman workers 170 may also occupy space within it. The obstacles 160 andworkers 170 need to be taken into account and avoided when the robots130 navigate the warehouse 100. Further detail of the system areprovided in a further US patent application with the title “A system andmethod for transporting inventory items in logistic facilities” filed onthe same date as the present document and incorporated herein byreference in its entirety.

The objective is to transport inventory items from one point within thewarehouse 100 to another point within the warehouse 100 using a singleor multiple robots 130. Some of the platforms 140 carrying suchinventory items may be of a nature that allows them being carried by asingle robot 130. Other platforms 140 in contrast can only be carried bymultiple robots 130, be that because of their size or their weight or acombination of both. The embodiment provides a means of coordinationamong multiple robots 130 to allow transport of platforms 140 also inthe later scenario. A central control unit 180 is provided forcontrolling the operation of robots 130.

FIG. 2 shows an example of a robot. In the embodiment each robot 130 hasa holonomic drive 210 and a vertically extendable lifting platform 200on its top surface. The holonomic drive 210 controls the movement of therobot 130, for example, as it moves within the warehouse 100. Thelifting platform 200 is configured to engage with a lifting location ofthe platform 140 during a lift operation.

Each robot 130 further comprises a wireless input/output port 220connected to an antenna 260 to transmit and receive signals. The robot130 may receive a signal from a control system covering the warehouse,such as a signal specifying a lifting position under the platform 140.The robot 130 may transmit a signal to the control system, such as asignal indicating that a load experienced by the robot 130 during a liftoperation is too big. In other embodiments, the robot 130 may receive ortransmit signals to and from other robots 130.

Each robot 130 further comprises a microprocessor 230 and a non-volatilememory 240. The processor 230 is configured to execute instructionsreceived from the control system, or another robot 130. The processor230 is also configured to execute instructions stored in thenon-volatile memory 240. Execution of these instructions causes therobot 130 to perform some of the method steps described herein. Forexample, execution of the instructions may cause a control module 250 inconjunction with the holonomic drive 210 to move the robot 130 to adesired location within the warehouse 100. The robot 130 furthercomprises sensors 270 that allow it to sense its environment, inparticular obstacles and human workers, under the control of theprocessor 230. Multiple different sensors, including image generatingsensors such as cameras and infrared sensors may be provided. In theembodiment the processor is configured to perform multi-sensory datafusion to derive different types of information, such as distancesbetween objects or distances of objects from the robot, orientation ofthe robot within its environment or relative to elements of theenvironment, etc. The use of such sensors and data processing eliminatesthe need for a global coordinate system for the robots 130. Each robot130 is moreover associated with a unique ID for wireless communication.

FIG. 3 shows an example of a central processing unit 180. The unitcomprises a processor 300 in communicative connection with non-volatilememory 310. Non-volatile memory 320 stores computer program instructionsthat, when executed, by the processor 300, cause the processor toperform the control functions of the central processing unit 180described herein. The processor 300 is further incommunicativeconnection with a wireless input/output unit 320 that allows theprocessor to establish wireless communication connections with otherelements within the warehouse, such as robots 130, using antenna 330.Additionally the controller 300 may wirelessly receive information fromsensors or scanners, for example a scanner that allow an operator toidentify a platform 140 that has been loaded with newly arrived goodsthat need to be stored in the warehouse. The central processing unit 180further comprises, in one embodiment, a user interface 340 that allowsthe user to input further information, such as a type of goods loaded onidentified platforms 140, platform identifiers, locations to which aplatform 140 is to be transported or retrieved from within thewarehouse, etc.

Discussing the individual steps in in realizing collective transport inmore detail, task information is transmitted from the central controlunit 180 to the robots (as illustrated FIG. 4a )). Such task informationmay specify a particular task to be performed by a number of robots, saymoving an inventory item from one location to another. The taskinformation may include any orders, data, instructions, commands orinformation structured in any appropriate form for the robots tointerpret in a manner that allows them to perform their tasks. Thecentral control unit 180 maintains task requests and disseminates thisinformation to the robots in the form of a system-wide broadcast.Alternatively, robots maintain status of platforms and task requests ina shared distributed database, which is continuously updated inreal-time based on sensory inputs of different robots.

The robots 130 can be in different states at different time, includingtwo baseline states: IDLE and BUSY. A robot 130 in the BUSY state isalready involved in transportation of inventory items or charging itsbattery, and therefore, it is not available for new tasks. Afterreceiving the task information, the IDLE robots 130 in the system engagein a leader election process, as illustrated in FIG. 4b ). A leader isthe best-fit robot 130 among the IDLE robots 130 based on anysystem-level metric. In an embodiment the robots use multi-hop meshcommunication so that the robots/vehicles in the system are aware oflocation and battery status information transmitted by fellowrobots/vehicles. On the basis of this information individualrobots/vehicles can determine whether or not they should designatethemselves as leader robot and are configured to do so in the event of apositive determination.

In one embodiment, the leader robot L is the one which is closest to thestart location of the task. However, moving inventory items acrosslogistic facilities consumes energy. Moreover, the leader robot would beengaged in coordinating the formation. Hence, in an alternativeembodiment, the leader robot is the one with the maximum batterylifetime. In a yet alternative embodiment, the leader robot is selectedthrough an optimization problem that ensures task delivery with maximumbattery lifetime subject to a minimum distance constraint. FIG. 5further elaborates on leader election based on distance and energyconstraints. For the sake of illustration, three robots 130 areconsidered in the leader election, robots C, D and F. Robots C and Fhave the same battery charge. Robot D has a lower battery charge thanrobots C and F. Although robot D is closer to the platform to betransported, robot C is elected as a leader as it has a higher batterylevel.

Once a leader has been elected, it recruits followers for completing thetask as illustrated in FIG. 4c ). If the platform/pallet can be handledwith a single robot only, the leader completes the task itself. If theplatform/pallet requires multiple robots, the leaderbroadcasts/advertises a ROBOTS_REQ message for recruiting followers.After receiving the ROBOTS_REQ message, robots volunteer for the task.In one embodiment, robots volunteer based on their distance from thestart location of the task. In a second embodiment, followers volunteerfor the task by taking into account the required energy consumption ofthe task. The exact number of required followers depends on the desiredformation for collective transport. Follower selection is illustrated inFIG. 4c ).

The formation synthesis and control requires group-based communicationbetween the leader and the follower robots. This communication has totake place locally as multiple formations can be operating in parallelin different parts of the facility. In the proposed framework, robotstaking part in the collective transport build a distributed schedule forgroup-based communication in the formation. The procedure for building adistributed schedule is shown in FIG. 6. The super-frame consists ofthree distinct frames: beacon frame, signalling frame, andgroup-communication frame(s).

Initially, the leader robot and the follower robots are timesynchronized. Each robot maintains a local timer, which are periodicallysynchronized through beacons received from the leader. This is achievedin the beacon frame.

The signalling frame, W_(s), which consists of a fixed number oftimeslots on a specific frequency channel, is used for informationexchange regarding schedule construction. The first signalling slot S₀is used by the leader to broadcast some schedule-related information. Inorder to build a schedule without contention, the downlink informationcontains information regarding the priorities for the follower robots.The leader robot is configured to randomly assign priorities to thefollower robots. Following the downlink slot, there is a repetitivepattern of two timeslots, first for a follower robot to requestresources (timeslots on distinct frequency channels) from the leaderrobot and the second for the leader to confirm the requested allocation.Such a leader-follower handshake ensures conflict-free scheduleconstruction for group communication.

In one embodiment, the group communication consists of downlinkcommunication from the leader robot to all followers in a broadcastfashion and uplink communication from each follower to the leader in aunicast fashion. In this case, a schedule is built for one-to-many(downlink) and many-to-one (uplink) communication. For the sake ofillustration, robots with lower IDs are treated as having a higherpriority. The downlink information from the leader informs followers ofthe next available slot for requesting resources. The follower robotsuse their priority information to determine their timeslot forrequesting resources. For the downlink broadcast scenario, the leaderselects the first available timeslot (t0) on the downlink channel forbroadcast information. Each follower robot selects a timeslot which isfree as per its local knowledge. For instance, the robot with ID number2 requests timeslot t1 on the uplink channel when rending a requestmessage in signalling slot s1. The leader confirms the requestedallocation (if and as this slot is not used by any other robot) bysending a response message in signalling slot s2. The robots with IDnumbers 3 and 4 follow a similar procedure and get allocated timeslotst2 and t3, respectively. For the downlink unicast scenario, the leaderselects timeslots t0-t3, with t0 dedicated for any broadcastinformation, and t1-t3 dedicated for communication with the robots withID numbers 2-4, respectively.

In an alternative embodiment, group communication consists of downlinkcommunication (in broadcast or unicast manner) and uplink communicationbetween the leader and the followers as well as neighbour-to-neighbourinformation exchange among follower robots. The schedule buildingprocess takes places through the aforementioned signalling. However, inthis case, follower robots request at least one extra timeslot forcommunication with at least one neighbouring follower robot, which isreferred to as the friend/relay robot and assists the follower robotduring formation synthesis and control. This embodiment is illustratedin FIG. 7. The schedule only needs to be constructed once for a giventask of collective transport. Hence, group communication for theformation can continue in a cyclic fashion from beginning of the task tothe end of task. The group communication procedure can be triggered oncethe leader and all the followers are in the vicinity of the platform tobe transported after leader election and follower selection process iscomplete. The leader and followers can be in different parts of thefacility; however, they are aware of the location of the platform.Hence, they can independently traverse toward the platform for formationsynthesis.

The robots 130 are configured to arrange themselves into one ofplurality of geometric patterns under a platform that is to be lifted,as required for the transport task that is to be performed. Eachgeometric pattern is characterized by a fixed number of positions, asshown in FIG. 8. The required geometric pattern may be communicated tothe robots as part of the task information. Alternatively one of therobots, for example the lead robot, may determine the nature/type of theplatform to be transported, for example by detecting a uniqueidentifier, such as a OR code or barcode of the platform using itssensors, and deducing from this identifier the formation to be adoptedby the robots. Further alternatively or additionally, robots maydetermine a new formation to be adopted following an unsuccessfulattempt to transport a platform. This may happen if an initiallydetermined number of robots in an initial formation do no manage totransport the platform, for example because the group of robots cannotlift the total weight of the platform or because the initially adoptedformation does not take into account an unbalanced load.

An objective of the mapping procedure is to allocate robots to differentpositions pertaining to the formation. In order to realizerobot-to-position mapping, the leader robot first generates a geometrymatrix for the formation to be formed. The exact geometric shape to beformed depends on the platform to be moved and its load distribution.The leader robot broadcasts the geometry matrix (illustrated in FIG. 9)to all the follower robots in the downlink. One way to realize thegeometry matrix is

$\begin{matrix}\begin{matrix}Q_{1} & Q_{2} & Q_{3} & \ldots & Q_{N} \\0 & d_{2} & d_{3} & \ldots & d_{N} \\0 & \theta_{2} & \theta_{3} & \ldots & \theta_{N}\end{matrix} & (1)\end{matrix}$

where each column refers to a position of the shape to be formed, withfirst row of each column containing the position, the second row of eachcolumn containing the distance and the third row of each columncontaining the orientation information. The distance and orientationinformation are in reference to the leader robot, which would beoccupying the first position.

In one embodiment, the mapping procedure is performed by the leaderrobot based on the feedback from the follower robots. The key steps ofthis mapping procedure (illustrated in FIG. 10) are described asfollows.

-   -   1. Leader robot broadcasts the geometry matrix (such as the        matrix (1) above) to be adopted by the robots to the follower        robots. This broadcast excludes details of the positions to be        adopted by specific individual robots.    -   2. Each follower robot measures its distance from each position        of the geometry matrix. The distance of the i^(th) follower        robot from the j^(th) position is denoted by H_(i,j).    -   3. Each follower robot transmits H_(i,j) along with its        remaining battery level to the leader robot in its assigned        uplink timeslot.    -   4. The leader robot finds the best position for each robot in        terms of minimal distance, or minimal energy consumption (for        task completion) or minimum cost jointly determined by distance        and energy consumption (for task completion).    -   5. The leader robot creates and broadcasts an allocation matrix,        which indicates robot-to-position mapping information as shown        below where the second row indicates the robot.

$\begin{matrix}\begin{matrix}Q_{1} & Q_{2} & Q_{3} & \ldots & Q_{N} \\L & 3 & 4 & \ldots & K\end{matrix} & (1)\end{matrix}$

In another embodiment, the follower robots negotiate their position inthe shape to be formed through local information exchange. Steps in thismapping procedure are:

-   -   1. The leader robot broadcasts the desired geometry matrix (such        as the matrix (1) above) to be adopted to the follower robots in        the downlink. This broadcast excludes details of the positions        to be adopted by specific individual robots. The leader robot        also informs robots that the first position is not available for        negotiation.    -   2. Each follower robot measures its distance from all available        positions and sends a negotiation start (NEG_START) message to        all the robots in its assigned timeslot.    -   3. Each follower robot listens to the NEG_START messages of        other robots.    -   4. At the end of the communication cycle, each follower robot        knows the distance of other follower robots from each position        of the shape to be formed.    -   5. Each follower robot assigns itself the position with the        smallest distance and communicates this to other follower robots        through a negotiation end (NEG_END) message during its assigned        timeslot on the next uplink cycle. The NEG_END message contains        an instance of the allocation matrix indicating the position        filled by the robot.

In another embodiment the above mentioned procedure is executed withenergy consumption metric or a cost function jointly determined bydistance and energy consumption. The procedure is executed over multiplecycles if more than one robot qualifies for a specific position.

In an embodiment the formation is synthesized in a sequential manner. Inan alternative embodiment the formation is synthesised in a parallelmanner. In the former case, each position of the formation is filled ina sequential way whereas in the latter case, multiple positions of theformation can be filled simultaneously. During the synthesis process,robots can be leader-referenced or neighbour-referenced, or leader aswell as neighbour-referenced. The synthesis process relies on areference matrix which provides the information about the reference foreach robot along with the distance and orientation information.

In one embodiment, the reference matrix is derived a priori by theleader robot as shown in FIG. 11. One way to realize the referencematrix is shown below where each column refers to the robots engaged incollective transport. Further each column is a vector that contains thereference robots, the distance (denoted by D) and orientationinformation (denoted by ψ) for each robot.

Leader Robot 2 . . . Robot N [ ] [L] . . . [L] 0 D₂ . . . D_(N, L) 0ψ_(2, L) . . . ψ_(N, L)

In another embodiment, the reference matrix is derived on-the-fly asshown in FIG. 12 for a diamond formation. The formation synthesisprocess begins with the leader robot moving towards the platform andaligning with a specific position, which becomes the first position ofthe formation. After aligning with the first position, the leader robotsends a position aligned (POS_ALGN) message to all the follower robots,as shown in FIG. 12. The POS_ALGN also contains a reference matrix withentries pertaining only to the leader robot, i.e., the first column.

Since robot 3 knows from the geometry matrix that it has to fill secondposition in the formation, it starts moving towards it after hearing thePOS_ALGN message from the leader robot. It selects the leader robot asthe reference and aligns itself in the second position at the desireddistance and orientation. After alignment, robot 3 sends a POS_ALGNmessage to all robots engaged in formation synthesis. The POS_ALGNmessage also contains updated version of the reference matrix withentries pertaining to robot 3. Robot 2 follows a similar procedure afterreceiving the POS_ALGN message from robot 3 while referencing itselfwith respect to the leader and aligning with position 3 at the desireddistance and orientation. After alignment, it sends the POS_ALGN to allrobots with updated version of reference matrix including entriespertaining to itself. Finally, robot 4 needs to fill position 4 of theformation. It has the latest version of the reference matrix and knowsthat the leader as well as robots 2 and 3 have already aligned in theirrespective positions. Instead of referencing a distant robot, a robotgives preference to a closer robot (as a reference), if available. Inthis case, we assume that robot 4 is closer to robots 2 and 3. Hence, itreferences both robots 2 and 3 and aligns itself in position 4 at thedesired position. After alignment, it sends a POS_ALGN message to allrobots engaged in formation. Once the leader receives POS_ALGN messagesfrom all follower robots, it sends a formation complete (FORM_CMPLT)message. The FORM_CMPLT message triggers the lifting mechanism at allrobots. Lifting is performed synchronously to ensure that the platformis carried in a stable manner.

The synthesized formation needs to be maintained while the platform isbeing transported from one point to another. This is illustrated in FIG.13. In one embodiment, only the leader robot is aware of the path thatwould be followed for transporting the object. For this purpose therobots maintain coupling/communication during movement, so that theformation moves smoothly as a unit which is particularly important forrobots with on-holonomic drives. Such virtual coupling can be achievedthrough closed-loop interaction between the leader and the followerrobots. The leader receives speed/velocity feedback from all followerrobots in the uplink and sends a new speed/velocity for each follower ifit is deviating (from leader's speed/velocity) by more than a certainthreshold. In an embodiment the leader robot has the path informationavailable as a set of reference points. In broadcasts the next referencepoint to all follower robots which compute the necessary speed/velocitycorrection (based on a kinematic model specific to the robot) formaintaining the required distance and orientation for a specific shape.

In another embodiment, the leader as well as all the follower robotshave knowledge of the path for transporting the platform. In this case,follower robots maintain the required distance and orientation from therespective referenced robot(s). The leader as well as the followerrobots periodically transmit a keep alive (K_ALIVE) message based on theschedule for group communication. The keep alive (K_ALIVE) message is aheartbeat message that may have an empty payload or comprise informationpertaining to the robot (e.g., its remaining battery level).

The formation of robots may encounter obstacles during collectivetransport. It is important that the formation stops as a whole if anyobstacle is detected by any of the robots. Timely delivery of suchevent-based control can also be achieved through the underlying groupcommunication schedule. The leader can stop the formation if it detectsan obstacle. This is achieved by an emergency stop (E_STOP) messagewhich is broadcast in the downlink. The follower robots can alsopiggyback information pertaining to obstacle detection on the uplinkinformation being exchanged over the group communication schedule. Basedon the received uplink information from any of the follower robots, theleader broadcasts an E_STOP message if it apprehends an obstaclecolliding with the formation.

It is possible that a robot fails during collective transport. In oneembodiment, this could be any of the follower robots. All robots areconfigured to send a warning signal (instead of a K_ALIVE message) tothe leader robot if it detects an issue that may lead to a failureduring collective transport. Upon receipt of the warning message theleader robot broadcasts an E_STOP message to all followers. The robotsstop and disengage the lifting mechanism in a synchronous manner. Therobot sending the warning signal is taken out of service and a formationreconfiguration procedure is triggered by the leader. Thereconfiguration procedure entails a suitable new formation for carryingthe platform. The leader robot generates a new geometry matrix as wellas a new reference matrix pertaining to the new shape. This isillustrated in FIG. 14. Whilst this figure illustrates are-configuration the robots in a geometry that requires one robot fewerthan the originally participating number of robots, the leader robot canalso advertise an emergence request to recruit a new follower robot toreplace the failed robot in the current or a different formation. Therequest for new follower contains position information for the newrobot, the reference robot(s) and the desired distance and orientationinformation.

Alternatively, if the leader robot fails during collective transport, itsends a warning signal to the followers and selects one of the followerrobots as the new leader robot. The new leader robot triggers theaforementioned reconfiguration procedure or it broadcasts an emergencyrequest for a new follower robot to replace the old leader (as afollower).

Embodiments discussed above consider energy cost of tasks to beperformed during follower selection process. This balances energyconsumption across the network and potentially maximizes networklifetime.

Embodiments described herein moreover facilitate simultaneous operationof multiple formations in different parts of the logistic facility.

Stable formation synthesis from any initial state of robots is moreoverfacilitated.

Group communication on fine timescale can ensure stability of theformation during collective transport.

The framework described herein moreover provides formationreconfiguration capabilities in case of robot failures.

In one embodiment the robots are configured to perform their allocatedtransport tasks solely based on origin and target location informationreceived from a central unit and on sensing information acquired by oneor more of the robots that form part of the group of robots allocated toa transport task. Put in other words, in the embodiment the group ofrobots does not need to receive any position or movement informationfrom the central unit beyond the information of the two locationsbetween which the transport task has to be performed. The robotstherefore do not need to rely on global knowledge of the environment inwhich they operate or on a global coordinate system or on any type ofinfrastructure support provided by a centralised management system. Therobots are in constant communication with each other during thetransport task so that sensing information acquired by one robot thatmay not be available to one or more other robots in the group (saybecause the robot's sensor(s) are obscured) is communicated within thegroup.

In the embodiment robots make decisions pertaining to formationsynthesis and control in a decentralized/distributed manner.

While certain arrangements have been described, the arrangements havebeen presented by way of example only, and are not intended to limit thescope of protection. The inventive concepts described herein may beimplemented in a variety of other forms. In addition, various omissions,substitutions and changes to the specific implementations describedherein may be made without departing from the scope of protectiondefined in the following claims.

1. A method performed in a system comprising a plurality of autonomousvehicles, the method comprising: a first vehicle transmitting ageometric configuration information to be adopted by one or more othervehicles participating in a transport operation in combination with thefirst vehicle, wherein the geometric configuration information comprisesinformation regarding respective distances and orientations the one ormore other vehicles are required to adopt relative to the first vehicle;a second vehicle, upon receipt of the geometric configurationinformation, adopting a position relative to the first vehicle or to afurther vehicle participating in the transport operation, the positionof the second vehicle defined by the geometric configurationinformation; and the first and second vehicles performing a transportoperation in a synchronised manner once the second vehicle has adoptedsaid position.
 2. A method as claimed in claim 1, wherein said one ormore vehicles, upon receipt of said geometric configuration information,return information indicating one or more of: a distance of theindividual vehicle to each location identified in the geometricconfiguration information or an amount of energy available to thevehicle; and wherein said first vehicle assigns an individual one of thefurther vehicles to each said location based on said returnedinformation.
 3. A method as claimed in claim 1, wherein said secondvehicles, upon receipt of said geometric configuration information,assigns itself to a location identified in the geometric configurationinformation based on at least one of: a distance of the second vehicleto the location, an amount of energy available to the vehicle or anestimated amount of energy required for the transport operation.
 4. Amethod as claimed in claim 1, wherein throughout the transport operationsaid first vehicle transmits movement information to other vehiclesparticipating in the transport information indicating a next movementrequired to be performed by the other vehicles, said movementinformation such that relative positions of the vehicles participatingin the transport operations are maintained whilst the vehicles performthe next movement.
 5. A method as claimed in claim 4, wherein saidmovement information comprise a velocity to be adopted by said vehiclesand wherein said vehicles feed a current velocity back to the firstvehicle.
 6. A method as claimed in claim 1, wherein one or more of thevehicles participating in the transport operation comprises a sensor orsensors for sensing one or more environmental conditions and a transmitfunction for communicating a sensed environmental condition to othervehicles participating in the transport operation.
 7. A method asclaimed in claim 5, wherein said first vehicle stops or pauses thetransport operation upon receipt of information from a vehicleparticipating in the transport operation indicating an environmentalcondition detrimental to continuing the transport operation.
 8. A methodas claimed in claim 1, wherein, upon receipt of information indicatingthat a vehicle that had previously participated in the transportoperation is not able to complete said transport operation, said firstvehicle either: instructs remaining vehicles participating in thetransport operation to adopt a geometric configuration suitable forcompletion of the transport operation and requiring a reduced number ofvehicles; or recruit a replacement vehicle for participation in thetransport operation.
 9. A method as claimed in claim 1, wherein saidvehicles participating in said transport operation communicate using atransmission schedule consisting of timeslots on distinct frequencychannels based on handshakes between the first vehicle and the vehiclesparticipating in the transport operation.
 10. A method as claimed in 1,wherein a vehicle participating in said transport operation selectsanother vehicle participating in the transport operation as a referencevehicle for maintaining a formation indicated by the geometricconfiguration information, wherein said selection is based oninformation received from other vehicles participating in said transportoperation.
 11. A system comprising a plurality of autonomous vehicles,the system comprising: a first vehicle configured to transmit geometricconfiguration information to be adopted by one or more other vehiclesparticipating in a transport operation in combination with the firstvehicle, wherein the geometric configuration information comprisesinformation regarding respective distances and orientations the one ormore other vehicles are required to adopt relative to the first vehicle;a second vehicle configured to, upon receipt of the geometricconfiguration information, adopt a position relative to the firstvehicle or to a further vehicle participating in the transportoperation, the position of the second vehicle defined by the geometricconfiguration information; and the first vehicle and the second vehicleconfigured to performing a transport operation in a synchronised manneronce the second vehicle has adopted said position.
 12. A system asclaimed in claim 11, wherein said one or more vehicles are configuredto, upon receipt of said geometric configuration information, returninformation indicating one or more of: a distance of the individualvehicle to each location identified in the geometric configurationinformation or an amount of energy available to the vehicle; and whereinsaid first vehicle is configured to assign an individual one of thefurther vehicles to each said location based on said returnedinformation.
 13. A system as claimed in claim 12, wherein said secondvehicle is configured to, upon receipt of said geometric configurationinformation, assign itself to a location identified in the geometricconfiguration information based on at least one of: a distance of thesecond vehicle to the location, an amount of energy available to thevehicle or an estimated amount of energy required for the transportoperation.
 14. A system as claimed in claim 11, wherein said firstvehicle is configured to transmit, throughout the transport operation,movement information to other vehicles participating in the transportoperation, the movement information indicating a next movement requiredto be performed by the other vehicles, said movement information suchthat relative positions of the vehicles participating in the transportoperations are maintained whilst the vehicles perform the next movement.15. A system as claimed in claim 11, wherein one or more of the vehiclesparticipating in the transport operation comprises a sensor or sensorsfor sensing one or more environmental conditions and a transmit functionfor communicating a sensed environmental condition to other vehiclesparticipating in the transport operation.
 16. A system as claimed inclaim 15, wherein said first vehicle is configured to stop or pause thetransport operation upon receipt of information from a vehicleparticipating in the transport operation indicating an environmentalcondition detrimental to continuing the transport operation.
 17. Asystem as claimed in claim 11, wherein the first vehicle is configuredto, upon receipt of information indicating that a vehicle that hadpreviously participated in the transport operation is not able tocomplete said transport operation, either: instruct remaining vehiclesparticipating in the transport operation to adopt a geometricconfiguration suitable for completion of the transport operation andrequiring a reduced number of vehicles; or recruit a replacement vehiclefor participation in the transport operation.
 18. A system as claimed inclaim 11, wherein said vehicles participating in said transportoperation communicate using a transmission schedule consisting oftimeslots on distinct frequency channels based on handshakes between thefirst vehicle and the vehicles participating in the transport operation.19. A system as claimed in 11, wherein a vehicle participating in saidtransport operation selects another vehicle participating in thetransport operation as a reference vehicle for maintaining a formationindicated by the geometric configuration information, wherein saidselection is based on information received from other vehiclesparticipating in said transport operation.
 20. An autonomous vehicleconfigured to: transmit geometric configuration information to beadopted by one or more other vehicles participating in a transportoperation in combination with the autonomous vehicle, wherein thegeometric configuration information comprises information regardingrespective distances and orientations the one or more other vehicles arerequired to adopt relative to the first vehicle.